[Hampshire] apt-get help needed please

Hi,

I am delving into the commandline on a new Ubuntu machine. It is a
VMWare virtual appliance, and I want to install webmin on it. I have
tried an apt-get update followed by apt-get install webmin which it
doesn't find. I have downloaded the .deb package directly from webmin
site, but I don't understand how I can get apt-get to pick up the
downloaded file.

Any help for me?

Regards
David